Genes Differentially Expressed During Tumor Progression

MRNA的差异显示已被用来确定其表达可能驱动或阻止肿瘤细胞表型进展的基因。其中一个这样的基因，金属蛋白酶组织抑制因子TIMP-3，在癌变前的JB6细胞中表达，但不在肿瘤性JB6细胞中表达(Sun等人，癌症Res，1994；Sun等人，J Biol Chem，1995)，并被发现在人DLD结肠癌细胞中表达时起到肿瘤抑制作用(Bian等人，癌症发生，1996)。TIMP-3的转录沉默可归因于其启动子的序列特异性甲基化(Pennie等人，Cell Growth and Diff，1999)。反义DNA甲基转移酶的表达恢复了肿瘤细胞中TIMP-3的表达，并概括了癌前病变JB6细胞中与TIMP-3表达相关的相同位点的非甲基化状态。进行了单独的差异显示分析，以确定可能调节或抑制肿瘤启动子依赖的进展阶段的基因表达。已分离到两个在抗启动子的小鼠JB6细胞中优先表达的基因的全长cDNA克隆。一个命名为pdcd4(Cmarik等人，PNAS 1999，是新的；另一个是plekstrin(Cmarik等人基因组学2000)。新基因pdcd4的反义表达将P-转化为P+细胞，pdcd4正义表达(Yang Et Al Oncogene 2001)将P+转化为P-细胞，从而建立了阻止肿瘤启动子诱导转化的因果关系。目前的研究主要集中在pdcd4蛋白的分子功能和定位上。对pdcd4对已知促进肿瘤所需的分子事件的可能抑制作用的研究表明，pdcd4的表达抑制了转录因子AP-1的激活，但不能抑制NFkappa B或鸟氨酸脱羧酶的激活(Yang Et Al Oncogene 2001)。虽然Pdcd4蛋白的表达阻断了AP-1的激活，但Pdcd4并不直接与Jun或Fos蛋白相互作用。通过酵母双杂交试验对pdcd4结合伙伴的分析表明，翻译起始因子之一是主要的结合伙伴。目前的研究集中在确定Pdcd4在调节蛋白质翻译中的功能意义，以及识别其翻译可能被Pdcd4表达抑制的特定转化相关的mRNAs。最后，我们发现染色质蛋白(S)HMGA1(Y)的表达是由肿瘤促进剂在促进敏感细胞中优先诱导的(Cmarik et al，Oncogene，1998)，并正在研究这一原因的意义以及HMGA1(现为HMGA1)作为转化相关AP-1靶基因的可能状态。

Differential display of mRNA has been used to identify genes whose expression may drive or prevent progression to tumor cell phenotype. One such gene, tissue inhibitor of metalloproteinases TIMP-3), was expressed in preneoplastic but not neoplastic JB6 cells (Sun et al., Cancer Res, 1994; Sun et al., J Biol Chem, 1995) and was found to act as a tumor suppressor when expressed in human DLD colon carcinoma cells (Bian et al., Carcinogenesis, 1996). The transcriptional silencing of TIMP-3 is attributable to sequence specific methylation of its promoter (Pennie et al., Cell Growth and Diff, 1999). Expression of antisense DNA methyl transferase restored expression of TIMP-3 to tumor cells and recapitulated the unmethylated status of the same sites associated with TIMP-3 expression in preneoplastic JB6 cells. A separate differential display analysis was carried out to identify gene expression that may mediate or inhibit tumor promoter dependent stages of progression. Full-length cDNA clones have been isolated for two genes preferentially expressed in promotion resistant mouse JB6 cells. One designated pdcd4 (Cmarik et al., PNAS 1999, is novel; the other is plekstrin (Cmarik et al Genomics 2000). Antisense expression of the novel pdcd4 gene converts P- to P+ cells and pdcd4 sense expression (Yang et al Oncogene 2001) converts P+ to P- cells, thus establishing a causal relationship to prevention of tumor promoter induced transformation. Current studies focus on the molecular function and localization of pdcd4 protein. Examination of the possible inhibitory effect of pdcd4 on molecular events known to be required for tumor promotion revealed that pdcd4 expression inhibited the activation of transcription factor AP-1 but not of NFkappa B or of ornithine decarboxylase(Yang et al Oncogene 2001). Although expression of Pdcd4 protein blocks AP-1 activation, Pdcd4 does not interact directly with Jun or Fos proteins. Analysis of pdcd4 binding partners by a yeast two-hybrid assay revealed one of the translation initiation factors as a major binding partner. Current research is focused on determining the functional significance of Pdcd4 in regulating protein translation and on identifying specific transformation relevant mRNAs whose translation may be inhibited by Pdcd4 expression. Finally, we have discovered that expression of the chromatin protein(s)HMG I(Y) is preferentially induced by tumor promoters in promotion sensitive cells (Cmarik et al, Oncogene, 1998), and are investigating the causal significance of this as well as the possible status of HMG I(Y) (now HMGA1) as a transformation relevant AP-1 target gene.